This specification relates to digital data processing and, in particular, to ranking of search results.
Internet search engines provide information about Internet accessible resources (e.g., web pages, images, electronic books, text documents, sounds, music, videos, electronic games, and multimedia content) by returning search results in response to queries. A search result includes, for example, a Uniform Resource Locator (URL) and a snippet of information for resources responsive to a query. The search results can be ranked (i.e., put in an order) according to scores assigned to the search results by a scoring function. The scoring function ranks the search results according to various signals, for example, where (and how often) query terms appear in the search results and how common the query terms are in the search results indexed by the search engine.